642 



BEDS OF TUFF AND LAPILLI. 



[Ch. XXV 



layers. 



I observed the following section near the amphi- 



November 



(descending series): 



1. Black sparkling sand from the eruption of 1822, containing 



Feet. Inches 



minute regularly formed crystals of augite and tourmaline 2£ 



2. 



Vegetable mould 



3 



3. Brown incoherent tuff, full of pisolitic globules, divided 



into layers, from half an inch to three inches m thickness . 



4. Small scoria and white lapilli .... 



5. Brown earthy tuff, with numerous pisolitic globules 



6. Brown earthy tuff, with lapilli divided into layers . 



7. Layer of whitish lapilli . 



8. Grey solid tuff ...... 



9. Pumice and white lapilli ..... 



1 6 



3 



9 



4 



1 



3 



3 



10 31 



seldom 



14 feet, and it is said that the higher part of the amphi- 

 theatre always projected above the surface ; though if this 

 were the case, it seems inexplicable that the city should 

 never have been discovered till the year 1750. It will be 

 observed in the above section, that two of the brown, half- 



consolidated tuffs are filled 



small pisolitic globules. 



circumstance 



Academy of Naple 



member 



strata incumbent on Pompeii. The mode of aggregation of 



Mr 



them formed in great numbers 



during the eruption on fine volcanic sand, and sometimes 



m 



minutest 



Their occur- 



emarl 



rence, thereiore, agrees remarKaoiy wen wnn tne d^uunv ^ 

 heavy rain, and showers of sand and ashes, recorded in 



t 



* Forbes, Ed. Journ. of Science, 

 No, xix. p. 130. 



f Scrope, Geol. Trans., second series, 

 vol. ii. p. 346. 



* 



v.] 





J eu 



•1 



i 



„jpor 



- ' 



th 







in 





• 



n 



wl 



, H 





the I 



• 



til 



Many of the ashes in these beds are vitrified, and harsh to o 



the tonch. Crystals of lencite, both fresh and farinaceous, 

 have been found intermixed.* The depth of the bed of 



N 







- 



re 

 rbc 



ta 



- 



iwithtr 

 li 



D 





P 



* ter. 



■Mi 



• 



a 



out. 



CO I 



,f 



r for* 



tl 







H 









I 



6d 





